1. Field of the Invention
The present invention relates generally to a visual inspection system and, particularly, but not exclusively, to a visual inspection system for inspecting leather hides.
2. Description of Related Art
The effect of damage caused to the hide of an animal during its lifetime is a major problem for the tanning industry. Such damage may result in defects existing in the processed leather hide, in the form of scars, abrasions and the like. The nature and quantity of defects existing in any particular hide will effect its application in the manufacture of leather goods. Areas of hide containing defects may be considered unusable, or useful only for particular purposes.
It is necessary to visually inspect each hide to determine the nature and distribution of defects, in order to "rank", the hide in terms of quality and sale price. Further, in the initial stages of manufacture of leather goods it is also necessary to inspect a hide to determine the location of non-defective areas which can be used in manufacture. For example, in the manufacture of shoes, shoe components of different sizes and shapes are "nested" within the hide geometry and cut manually using dies and a swing beam press. In the nesting and cutting operations, the operator must avoid defects.
Visual inspection of the hide, both for ranking and nesting/cutting, is presently carried out manually by skilled operators.
In the ranking process, an assessment is made of the degree to which the existent damage will effect the cutting yield, and the hide is priced accordingly. This assessment is of necessity subjective, based on the operators skill and experience. A subjective analysis can lead to non-uniformity in ranking between respective operators, and has resulted in disputes between tanners, pricing the hide, and leather goods manufacturers, purchasing the hide. In Australia, rates of return of hides from leather goods manufacturers to tanners as a result of disputes over ranking of hides run as high as 15% and result in disruption in production schedules and costs to both the manufacturer and tanner.
In the nesting/cutting process, a skilled operator attempts to achieve both optimum layout of patterns for components of leather goods and avoid defects unsuited for manufacture of the particular leather goods. This is an almost impossible task. Wastage of 34%. on average of raw material is common, in Australia. Further, under current manual cutting methods, the variation in yield between operators is in the order of 10%, depending upon the skill of the particular operator.
An automated visual inspection process, which may provide a more objective approach, may save operator costs and provide for more efficient utilization of material, is therefore desirable. Development of an automated system presents a number of problems, however.
Leather hide and like materials are non-rigid or "floppy". Any imaging device would have difficulty obtaining an accurate image of defects and distinguishing from shadows cast by raised or lowered areas of the hide caused by the "floppiness". Further, certain types of defects in animal hide may be invisible unless the hide is deformed before viewing. Such defects include scars which have become "sealed" because they healed in the animals lifetime. Present examination for sealed scars involves the operator stretching the hide over his finger to make the sealed scars more visible. This presents a significant hide manipulation problem for any proposed automatic process.
Difficulties also lie in processing an image from an imaging device to distinguish between defective and nondefective areas of a hide.